Chain-tensioner with mechanical locking

ABSTRACT

A tensioner for endless driving elements, such as chains and belts, comprising a tensioning piston provided with locking means, and a locking piston which is adapted to be engaged with and disengaged from the locking means so as to arrest or release the movement of tensioning piston, the locking piston comprising an operating section causing locking piston to move to the arresting position and to the release position, and a locking area used for engagement with the locking means of the tensioning piston and arranged separately from the operating section.

FIELD OF THE INVENTION

The present invention relates to a tensioner for endless drivingelements, such as chains and belts, and particularly a tensioner havinga tensioning piston provided with locking means, and a locking pistonwhich is implemented such that it is adapted to be engaged with anddisengaged from the locking means so as to arrest or release themovement of the tensioning piston.

BACKGROUND OF THE INVENTION

Such a tensioner is known e.g. from EP 0 657 662 A 2. This chaintensioner comprises a tensioning piston having a plurality of lockinggrooves on the outer circumference thereof, the locking grooves beingengaged by a spring-loaded locking piston. The front face of the lockingpiston is beveled and can be acted upon by an oil pressure so as todisengage the locking position. The locking means guarantees that alocking effect is produced when the engine oil hydraulic system isswitched off and that the locking piston can no longer retract. This hasthe effect that a certain pretension is maintained, even if the engineis at rest, in spite of possible oil leakage from the pressure chamber.Hence, a predetermined tension, which is independent of the engine oilhydraulic system, will exist when the engine is started. As soon assufficient pressure has built up, the locking means will be disengagedand the tensioning piston will operate in the usual way.

A similar tensioner is known e.g. from DE 195 48 923 A1. In addition,conventional locking devices are provided on chain tensioners and thelike, but these locking devices only serve to carry out a readjustmentand to limit the retraction path of the tensioning piston to apre-determined value. Such structural designs are used for wearcompensation. Locking de-vices connected to the engine oil hydraulicsystem are disadvantageous insofar as they are subjected to thefluctuations of the hydraulic pressure and to a possible pressurebuild-up in the area of the tensioning piston. In the case ofconventional locking devices, the locking piston is forced back by theteeth on the tensioning piston against the force of a spring, and thiswill entail wear.

It is therefore the object of the present invention to improve thestructural design of a tensioner of the type used with chaims and belts.

In accordance with the present invention, this object is achieved by thefeatures that the locking piston comprises an operating section causingsaid locking piston to move to the arresting position and to the releaseposition, and a locking area used for engagement with the locking meansof the tensioning piston and arranged separately from the operatingsection. Due to the fact that the operating point of the locking pistonand the point of engagement are separated from one another, it is nolonger necessary that the locking area is acted upon by operating forcesso as to disengage the locking piston. In the case of hydraulicallyoperated tensioners this means e.g. that the locking area of the lockingpiston need no longer be exposed directly to the engine oil hydraulicpressure. Actuation in one direction (arresting position) as well as inthe other direction (release position) takes place at some other point.A great variety of operating mechanisms for achieving a piston movementcan be employed. This separation of the locking function and of theoperating function also permits the locking piston to be controlled in apurposeful manner in dependence upon the operating parameters.Conventional locking devices of the readjustment type as well as lockingdevices which are readjustable by an engine oil hydraulic system arealways provided with operating means acting directly on the lockingarea.

According to an advantageous embodiment, the operating section of thelocking piston can be provided with a piston area which is adapted tohave applied thereto an operating pressure of a hydraulic fluid, theoperating direction of the piston area being directed towards therelease position of the locking piston. This measure has the effect thatthe locking piston will be displaced to the release position in responseto application of a hydraulic pressure. Such a structural design couldbe used in internal combustion engines and connected to the engine oilhydraulic system.

In accordance with a preferred embodiment, a spring means can beprovided, which acts on the operating area of the locking piston andwhich is effective in the direction of the arresting position of thelocking piston. This measure has the effect that the locking piston isprimarily forced into the arresting position by the spring force of thespring means. This means that an operating force in the oppositedirection must always be larger so as to cause unlocking.

According to an advantageous embodiment, the locking area of the lockingpiston can be designed such that a hydraulic force balance is caused.Such a structural design allows the locking area of the locking pistonto be subjected to a pressure medium, without the pressure mediumcausing any essential force component on the locking area for operatingthe locking piston. A person skilled in the art knows that, in order toachieve this, he must cause forces to act in opposite directions so thatthese forces will compensate each other (as far as the actuation isconcerned). Hence, such a tensioner could definitely be arranged in thepressure chamber of the tensioning piston; pressure fluctuations of thepressure in the pressure chamber will not have any influence on theoperation of the locking piston, neither into the arresting position norinto the release position. In hitherto used devices comprisingcontrolled locking devices, such pressure fluctuations have alwaysprevented the locking piston from moving immediately to its arrestingposition, when e.g. the engine hydraulic system had been switched off.The locking effect only occurred when the pressure had been reduced to acertain extent by leakage at the locking area of the locking piston.Such a delay is prevented by the structural design chosen.

In accordance with an advantageous embodiment, the locking area can beprovided in the form of a locking opening in a locking plunger whichextends away from the operating section, at least a portion of thelocking means of the tensioning piston extending through the lockingopening. The locking opening guarantees that a pressure medium in itsinterior will produce force components over the whole area of theopening and that the forces will compensate each other in such a waythat the actuation of the locking piston will not be supported. This isa simple structural measure by means of which the locking area can bedesignated such that is not subjected to the influence of pressureforces.

In addition, the locking opening may be provided with a lockingprojection, which is arranged on the inner surface of the lockingopening on one side thereof and which is used for engagement with thelocking means of the tensioning piston. Such a locking projection on theinner side does not have any influence on the force conditions in theoperating direction of the locking piston and guarantees nevertheless areliable engagement with the locking means of the tensioning piston.

According to one variant, the locking means of the tensioning piston maycomprise a lock-ing rod provided with teeth and extending through thelocking opening of the locking piston. The operating paths of thetensioning piston and of the locking piston will therefore cross andindividual components of the two pistons will interengage. A verycompact and very robust structural design is provided in this way.

The locking rod can have a circular basic cross-section, the lockingopening in the locking plunger being then implemented as an elongatedhole which is adapted to this basic cross-section. This length (seen inthe direction of the longitudinal axis of the locking piston) of theelongated hole can then correspond to at least to the operating strokeof the locking piston between the release position and the arrestingposition. This means that the locking rod and the locking piston partproviding the locking opening can also mutually guide themselves, sincethe amount of play must be chosen precisely such that the locking rodcan be dis-placed freely in the elongated hole in the release position.In the case of such a variant, the locking rod can also be implementedas an extension of the actual tensioning piston having a smallerdiameter. However, also other cross-sections are possible instead of thecircular cross-section.

When, in accordance with one variant, the inner surface of the lockingopening is provided on one side thereof with an undercut portion whichmerges with the locking projection, the locking opening provides also inthe arresting position a contact shoulder for close contact with thelocking rod. When the locking piston is implemented as a plasticcomponent or as a cast member, this undercut portion will also reducethe accumulation of material.

In accordance with one embodiment, the tensioning piston is guided in ahousing, a pressure chamber is formed between the housing and thetensioning piston, the locking means extend from the inner to the outerside of the pressure chamber, and the teeth are located outside of thepressure chamber in the fully retracted position of the tensioningpiston. This is to be regarded as an additional measure for displacingthe locking area of the locking piston away from the pressure area of afluid-operated tensioning piston. Depending on the structural design ofthe housing, the locking area will then only be subjected to a leakageflow of the fluid. Oscillating conditions occurring in the pressuremedium during operation of the tensioning means will therefore notaffect the locking piston.

According to a preferred embodiment, the locking piston can be guided ina housing such that it is separated from a pressure chamber of thetensioning piston. The two pistons can also be arranged in a commonhousing; in this case, only the locking means and the locking area crosseach other and are adapted to be brought into engagement with oneanother.

According to a further embodiment of the tensioner for an internalcombustion engine hav-ing an engine oil circuit, the piston area of thelocking piston can be acted upon by the hy-draulic pressure of theengine oil circuit. By selecting an advantageous supply means, it canhere be guaranteed that hydraulic oscillations of the type occurring inthe area of the pres-sure chamber of the tensioning piston are decoupledas far as possible from the operation of the locking piston. In thesimplest case, this delimitation is effected via a non-return valve.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, an embodiment of the present invention will beexplained in detail making reference to a drawing, in which:

FIG. 1 shows a hydraulic chain tensioner according to the presentinvention in a fully sec-tional view,

FIG. 2 shows the chain tensioner of FIG. 1 in a sectional view alongline II—II and

FIG. 3 shows the chain tensioner of FIG. 1 in a sectional view alongline II—II.

DETAILED DESCRIPTION OF THE INVENTION

The chain tensioner 1 shown in FIG. 1 to 3 is provided with a lockingfunction, in particular when the hydraulic circuit is switched off.

The chain tensioner 1 essentially comprises a cast housing 2 whichconsists e.g. of an aluminium die casting, a tensioning piston 3 whichis axially guided in the housing 2, and a locking piston 4 which isguided in the housing 2 at right angles to the tensioning piston 3. Thetensioning piston 3 is guided in a cylindrical bore 5 in the housing 2and comprises a cylindrical guide sleeve 6 and a piston head 7press-fitted into the guide sleeve 6 and consisting e.g. of a suitableplastic material. The guide sleeve 6 is preferably produced from steel.A portion of the piston head 7 rests on the end face of the guide sleeve6 so that it is guaranteed that an endless driving element, e.g. achain, or the tensioning area of a tensioning rail will come intocontact only with the piston head 7. In the interior of the guide sleeve6, the piston head 7 merges with a cylindrical locking rod 8 having, atthe free end thereof, locking teeth 9 acting as locking means. Thelocking teeth are implemented as a circumferentially extending annulargroove having a triangular cross-section, so that a sawtooth profile isformed in cross-section. The direction of the sawtooth profile is chosensuch that an extension, but not a retraction, of the tensioning piston 3can be blocked. Between the piston head 7 and the locking rod 8 ahollow-cylindrical annular space 10 is provided in the middle area ofthe locking rod 8, said annular space having arranged therein a helicalcompression spring (not shown). The compression spring rests on the back11 of the piston head 7 and on the base 12 of the bore 5.

The chain tensioner 1 is shown at a position of transport. At thisposition, the tensioning piston 3 is fully retracted and arrested by asecuring pin 12. The compression spring, not shown, in the annular space10 is compressed in its maximum tensioning condition. When the chaintensioner 1 has been installed with the aid of the fastening sleeves 13and 14 on the housing 2, the securing pin 12 is removed, whereby thetransport position will be re-leased. The tensioning piston 3 is then intensioning contact with e.g. the contact area of a tensioning rail,which, in turn, is pressed against a chain.

From the sectional view of FIG. 3 it can be seen that the annular space10 and the free space of the bore 5 extending below the tensioningpiston 3 can communicate via a hydrau-lic channel 37 in the housing 2with the engine oil hydraulic system of an internal combustion engine towhich the chain tensioner 1 is secured. This means that engine oil canflow into this pressure chamber via a non-return valve 36. The hydraulicfluid flows into the hy-draulic channel 37 via the non-return valve 36which is press-fitted into a lateral bore 38 of the housing. Thishydraulic channel extends parallel to the locking teeth 9 and parallelto the bore 29 in the bottom. Also a locking plunger 16 extends in thishydraulic channel 37 so that both the locking plunger 16 and the lockingteeth 9 on the locking rod 8 are subjected to the hydraulic pressure.Due to the displaced section along line II—II, the non-return valve 36is shown in FIG. 2 in a view which is only a fragmentary sectional view.In the operating state, the tensioning function is primarily applied bythis hydraulic pressure whose force exceeds the tensioning force of thespring. The hydraulic fluid in the pressure chamber is thereforesubjected to the vibrations of the tensioning piston 3 and relief onlytakes place via leakage flows. When the engine oil hydraulic pressureincreases, the tensioning force of the tensioning piston 3 will increaseas well.

The locking piston 4, which is displaceable in the housing 2 at rightangles to the tensioning piston 3, comprises a cylindrical operatingsection 15 and a locking plunger 16 arranged on said operating section15. Only the locking plunger 16 crosses the locking rod 8 of thetensioning piston 3. The operating section 15 is provided with anannular piston area 17. In addition, said operating section 15 is guidedin a cylindrical bore 18 such that it is axially displaceable therein.Between the piston area 17 and the base area 19 of the operating sectiona pressure chamber 20 is defined, which communicates via a supplypassage 21 with the engine oil hydraulic system. It follows that, whenpressure is built up in the pressure chamber 20, this will have theeffect that the locking piston 4 is displaced upwards (cf. FIG. 1) to arelease position. In the unloaded condition, the locking piston 4 ispressed down-wards into an arresting position (cf. FIG. 1) via acompression spring 22 which is arranged in a cylindrical bore 23 of theoperating section 15 and which rests on a support disk 24 se-cured by aretainer ring 25, said cylindrical bore 23 being open at the rear. Thespring force is dimensioned such that, in the operating state, it willbe bridged by the pressure in the pressure chamber 20.

The locking plunger 16 is rectangular in cross-section and extends in aguide opening 26 through the housing 2 and projects beyond the housingon one side thereof. In addition, the locking plunger 16 is providedwith hollow spaces 27, which permit the locking plunger 16 to be alsoimplemented as an injection-molded part consisting of plastic materials(so as to avoid accumulations of material).

The bore 5 for the tensioning piston 3 and the guide bore 26 for thelocking plunger 16 communicate only via a small connection opening 28,which is just large enough to permit passage of the portion of thelocking rod 8 provided with the locking teeth 9, and the hydraulicchannel 37. The free end of the locking teeth 9 is received in anddisplaceably guided in the bore 29 in the bottom of the housing 2.

The locking teeth 9 of the locking rod 8 extend through a lockingopening 30 provided in the locking plunger 16. This locking opening 30extends at right angles to the operating direc-tion of the lockingpiston 4. The inner circumference of the locking opening is fullydefined by the locking plunger 16 so that said locking opening can onlybe engaged from the left or from the right (cf. FIG. 1). In addition,when seen in a cross-sectional view, the locking open-ing 30 isimplemented as an elongated hole, which is adapted to thecross-sectional shape of the locking teeth 9 of the locking rod 8. Thelength of said elongate hole is chosen such that it exceeds the lengthof the operating path of the locking piston 4. The locking opening isprovided on one side thereof with an undercut portion 31 whosecross-section is, how-ever, designed such that, at the arrestingposition, the locking teeth 9 of the locking rod 8 will come intocontact with a shoulder 32 of the locking opening so that the undercutportion 31 will remain free. On one side of the locking opening 30, alocking projection 33 projects partly into said undercut portion 31 andpartly into said locking opening 30. The end face of said lockingprojection 33 has an arcuate form so that it will precisely fit inbetween the lock-ing teeth 9. The locking projection 33 is designed suchthat it is adapted to be brought into engagement with a respectiveannular groove between the teeth of the locking teeth 9. Also saidannular groove is triangular in cross-section, the part of said groovemerging with the undercut portion 31 being, however, rounded.

At the side of the bore 18, a vent channel 34 is arranged through whichalso a leakage flow can escape from the pressure chamber 20.

In the following, the mode of operation and the function of the chaintensioner 1 will be ex-plained in detail.

The locking teeth 9 of the locking rod 8 extend through a lockingopening 30 provided in the locking plunger 16. This locking opening 30extends at right angles to the operating direction of the locking piston4. The inner circumference of the locking opening 30 is fully defined bythe locking plunger 16 so that the locking opening can only be engagedfrom the left or from the right (cf. FIG. 1). In addition, when seen ina cross-sectional view, the locking opening 30 is implemented as anelongated hole, which is adapted to the cross-sectional shape of thelocking teeth 9 of the locking rod 8. The length of the elongate hole ischosen such that it exceeds the length of the operating path of thelocking piston 4. The locking opening is provided on one side thereofwith an undercut portion 31 whose cross-section is, however, designedsuch that, at the arresting position, the locking teeth 9 of the lockingrod 8 will come into contact with a shoulder 32 of the locking openingso that the undercut portion 31 will remain free. On one side of thelocking opening 30, a locking projection 33 projects partly into theundercut portion 31 and partly into the locking opening 30. The end faceof the locking projection 33 has an arcuate form so that it willprecisely fit in between the locking teeth 9. The locking projection 33is designed such that it is adapted to be brought into engagement with arespective annular groove between the teeth of the locking teeth 9. Alsothe annular groove is triangular in cross-section, the part of saidgroove merging with the undercut portion 31 being, however, rounded.

Assuming now that the internal combustion engine is switched off, thetensioning piston 3 and the locking piston 4 will not have appliedthereto any hydraulic pressure. In this condition, the tensioning piston3 is prevented from retracting by the locking piston 4, which is forcedinto the arresting position by the compression spring 22. This meansthat, when the engine is being started, a retraction of the tensioningpiston 3 will be prevented in spite of strong forces occurring at thepiston head 7, before a suitable hydraulic pressure can build up in thehydraulic circuit. It follows that, in spite of the insufficienthydraulic pressure, a predetermined tension will always be given whenthe engine is started. As soon as a sufficient hydraulic pressure hasbuilt up after the start of the engine, the locking piston 4 will bedisplaced to the release position due to the pressure that builds up inthe pressure chamber 20. Also the hydraulic pressure in the pressurechamber of the tensioning piston 3 is increased such that the tensioningforce will be applied mainly through this hydraulic pressure. Thishydraulic pressure is load-dependent and increases in the case of higherspeeds, whereby the tension will be increased. In this condition, thetensioning piston 3 can operate in the normal way, as in the case ofconventional hydraulic chain tensioners. The locking teeth 9 can movefreely within the locking opening 30 because the locking projection 33is retracted. Also hydraulic fluid penetrates into the locking opening30 through the connection channel 37 and the connection opening 28. Dueto the fact that the locking opening 30 is implemented as acircumferentially closed elongated hole, the hydraulic pressure will,however, not influence the operation of the locking piston 4. On thecontrary, force components will be generated both towards the releaseposition and towards the arresting position so that the hydraulicpressure will not influence the operating behavior of the locking piston4 within the locking opening 30. Nor do the undercut portion 31 and thelocking projection 33 produce any effect in the operating direction,since what matters is the area projected perpendicularly to theoperating direction. It follows that the operation of the locking piston4 is only influenced by the compression spring 22 and the hydraulicpressure in the pressure chamber 20. The pressure chamber 20 is,however, decoupled from the pressure chamber of the tensioning piston 3and its pressure fluctuations caused by vibrations on the endlessdriving element, e.g. the chain. A reliable extension and retractionbehavior of the locking piston 4 is achieved in this way.

According to a further embodiment, the locking piston could also beoperated electrically or pneumatically.

1. A tensioner (1) for endless driving elements, comprising: atensioning piston (3) provided with locking means (8, 9); and a lockingpiston (4) which is adapted to move between an arresting positionengaged with said locking means (8, 9) to arrest the movement of saidtensioning piston (3) and a release position disengaged from saidlocking means (8, 9) to release the movement of said tensioning piston(3), the locking piston (4) having an operating section (15) causing thelocking piston (4) to move to the arresting position and to the releaseposition, and a locking area (30, 33) used for engagement with thelocking means (8, 9) of the tensioning piston (3) and arrangedseparately from the operating section (15), the locking area (30, 33) ofthe locking piston (4) being designed such that a hydraulic forcebalance is caused wherein the locking area is provided in the form of alocking opening (30) in a locking plunger (16) which extends away fromthe operating section (15), and at least a portion of the locking means(8, 9) of the tensioning piston (3) extending through the lockingopening (30).
 2. A tensioner (1) according to claim 1, wherein theoperating section (15) of the locking piston (4) is provided with apiston area (17) which is adapted to have applied thereto an operatingpressure of a hydraulic fluid, the operating direction of the pistonarea (17) being directed towards the release position of the lockingpiston (4).
 3. A tensioner (1) according to claim 1, further comprisinga spring means (22), which acts on the operating section (15) of thelocking piston (4), the spring means (22) being effective in thedirection of the arresting position of the locking piston (4).
 4. Atensioner (1) according to claim 1, wherein the locking opening (30) isprovided with a locking projection (33), which is arranged on the innersurface of the locking opening (30) on one side thereof and which isused for engagement with the locking means (8, 9) of the tensioningpiston (3).
 5. A tensioner (1) according to claim 1, wherein the lockingmeans (8, 9) of the tensioning piston (3) comprises a locking rod (8)provided with teeth (9) and extending through the locking opening (30)of the locking piston (4).
 6. A tensioner (1) according to claim 5,wherein the locking rod (8) has a circular basic cross-section, and thelocking opening (30) is implemented as an elongated hole which isadapted to the basic cross-section, the length of the elongated holecorresponding at least to the operating stroke of the locking piston (4)between the release position and the arresting position.
 7. A tensioner(1) according to claim 6, wherein the inner surface of the lockingopening (30) is provided on one side thereof with an undercut portion(31) which merges with the locking projection (33).
 8. A tensioner (1)according to claim 5, wherein the tensioning piston (3) is guided in ahousing (2), a pressure chamber is formed between the housing (2) andthe tensioning piston (3), the locking means (8, 9) extends from theinner to the outer side of the pressure chamber, and the teeth (9) arelocated outside of the pressure chamber, at least in the fully retractedposition of the tensioning piston (3).
 9. A tensioner (1) according toclaim 1, wherein the locking piston (4) is guided in a housing (2) suchthat it is separated from a pressure chamber of the tensioning piston(3).